Dean on mon 13 jun 11
Aloha all:
I've been making bowls and cups from multi-layered colored porcelain (Dave'=
=3D
s porcelain from Laguna).=3DA0 The bowls are about 6" high inverted cone sh=
ap=3D
ed and they crack horribly on drying. They're thin, about 1/8" and I'm dryi=
=3D
ng them slowly under plastic. I've lost four out of nine so far (2 still un=
=3D
der plastic), almost a week's work, aaaugghh!=3DA0 The cracks go from the r=
im=3D
to the base and separate and open up as much as an inch at the top. What a=
=3D
m I doing wrong?=3DA0 Anyone have any thoughts on this?=3DA0=3D20
Mahalos,
Dean
LightWavepottery.com
ivor and olive lewis on tue 14 jun 11
Dean,
I take it that you are forming your bowls from a circle of clay that has ha=
d
a segment (pie shape) removed.
Your pots may be failing during drying because your method of joining the
radial edges of the clay slab does not weld clay to clay. Are you using a
butt joint or a lapped joint ?
This seems to be one of those situations where illustrations would prove
useful.
Best regards,
Ivor.
'
Ivor Lewis,
REDHILL,
South Australia
David Woof on tue 14 jun 11
Hi Dean=3D2C
=3D20
If you ask yourself enough questions about your work and work methods=3D2C =
th=3D
e answer will come.
What is the orientation of the layers?
Are the cracks following a seam of differing colors? What is your joining =
=3D
technique?
Is there more than one crack per bowl?
=3D20
My next thought would be is that you have a drying problem. (Actually the =
=3D
foregoing technical concerns are usually exacerbated by or reduced to dryin=
=3D
g problems as well.) =3D20
Are you drying the forms inverted?
=3D20
If you have thin fragile rims you may have to get creative to keep the rims=
=3D
from drying faster than the rest of the bowl.
=3D20
What would painting the upper 1/4 of the bowl with wax resist=3D2C and dryi=
ng=3D
the bowl from the bottom up by tenting it with plastic and setting it on a=
=3D
open grid rack for air access from underneath do? Why would you do this?
=3D20
If this mars the bottoms unacceptably=3D3B could you wax the rim and invert=
t=3D
he bowl after stuffing it with enough soft plastic material to cause the ri=
=3D
m to ride above the table surface?
=3D20
The bottoms must dry faster than the rim or the rims "lock" and the ensuing=
=3D
tension as the bottom dries causes the stress cracks that plague folks tha=
=3D
t don't take measures to address this problem.=3D20
=3D20
Your bowls sound like fun to make.=3D20
=3D20
Best to all=3D2C
=3D20
David Woof
___________________________________________________________________________=
=3D
___--
4. slab bowl cracks
Posted by: "Dean" mangodean@YAHOO.COM=3D20
Date: Mon Jun 13=3D2C 2011 6:58 pm ((PDT))
Aloha all:
I've been making bowls and cups from multi-layered colored porcelain (Dave'=
=3D
s porcelain from Laguna). The bowls are about 6" high inverted cone shaped=
=3D
and they crack horribly on drying. They're thin=3D2C about 1/8" and I'm dr=
yi=3D
ng them slowly under plastic. I've lost four out of nine so far (2 still un=
=3D
der plastic)=3D2C almost a week's work=3D2C aaaugghh! The cracks go from t=
he r=3D
im to the base and separate and open up as much as an inch at the top. What=
=3D
am I doing wrong? Anyone have any thoughts on this? =3D20
Mahalos=3D2C
Dean
LightWavepottery.com
=3D20
=3D20
=3D
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